This invention relates to computer screen displays and electronic light pens for use therewith. Specifically, this invention relates to light pens that use the light emanating from a display screen, such as a computer screen, television, or LCD display, to determine the position of the tip of the light pen with respect to the display screen.
Pointing devices of various types are used in almost every computer application today. The popularity of graphic based operating systems such as those popularly employed by Apple Corporation or by the various manufacturers of computers using WINDOW(trademark) operating systems, have resulted in the development of a number of pointing devices to be used in conjunction with the display screen of the computerized device. Some of the pointing devices that have been developed and popularized include:
(1) a mouse;
(2) a trackball;
(3) a transparent-touch screen that overlays the display including resistive and capacitive types;
(4) pressure, capacitive, resistive, or thermal sensitive tablet separate from the display;
(5) beam-breaking detectors surrounding the display;
(6) a light pen based on detection of the raster scan timing of the phosphor refresh beam;
(7) a stylus that incorporates pressure transducers; and
(8) a pen using ultrasonic, stereo tactic or radio frequency triangulation methods.
The various devices developed to position a pointer on a computer screen operate in conjunction with the application software on the computer using an appropriate xe2x80x9cdriverxe2x80x9d. Most such drivers try to emulate the conventional X/Y roller xe2x80x9cmousexe2x80x9d which is very commonplace. Typically, only positional information is fed to the application software that controls the position of the pointer on the screen.
Light pens operate through use of a photo-detector typically located adjacent to the tip of the pen. Typically, the position of the pen with respect to the computer display is determined by timing the response of the photo-detector with the horizontal and vertical retrace of the display. The very high energy phosphor refresh beam illuminates the photodiodes substantially above the ambient screen brightness level. By reading a counter synchronized to the timing of the refresh beam, the position of the photo detector may be determined with a quite reasonable degree of accuracy. Unfortunately, the sampling rate is determined by the screen refresh rate; and accordingly, the sampling rate is quite limited as typical screen refresh rates are less than one hundred cycles per secondxe2x80x94usually, between 60 and 72 hertz. That means that very fine movement of the light pen, or continuous movement such as in handwriting, may be undetected or only approximated.
Further, light pens are completely ineffective with liquid crystal displays. Also, present light pen technology requires expensive counters and additional circuitry to be effective with television displays, projection displays, and passively lit technologies.
Another prevalent problem is that external sensors are required for many of the above listed prior art pointing devices. Touch screens are expensive and bulky in contrast to the market""s desire for small, inexpensive and portable touch screen systems.
Touch screens and tablets are limited in resolution to the sensor resolution. Typically, touch screens and tablets have a resolution that is much more coarse than the screen resolution of the computer for which they are acting as an input device, and accordingly the full resolution of the display is not taken advantage of. Also, touch screens and tablets have a scan matrix speed limitation similar to a computer keyboard.
A pressure sensitive writing tablet also has the additional limitation or disadvantage of being physically separated from the display screen of a computer. Accordingly, it is not possible to visually fixate on the writing tablet, where writing is taking place, and also visually fixate on the display screen, where the end result of the writing is being displayed, at the same time. It is therefore not possible to produce completely natural writing with a pressure sensitive writing tablet.
One example of the limitations of presently available prior art pointing devices can be found in modern electronic medical devices. Use of electronic patient records is becoming increasingly popular in modern medicine. Many of the devices and methods that are presently used rely on original paper-based technologyxe2x80x94that is to say, paper printouts are relied on so that doctors can examine and write on the paper printouts. Two specific examples of state of the art medical technology that are still primarily paper based include EEG (electroencephalography) and ECG (electrocardiography) systems. Large numbers of EEG, ECG, and other paper records are generated every day in hospitals, doctors"" offices, and clinics throughout the world. The electronic instrumentation and data are computerized, but physicians typically are much more comfortable holding a piece of paper in their hands. This is disadvantageous for EEG and ECG situations in particular, as physicians typically annotate these records at points of interest on the paper record, and include these marked up copies as part of a patient""s record. Electronic systems exist at a basic stage, where various charts, data, pictures, and the like, are displayed on a color display screen; however, it is necessary to use a mouse and keyboard input devices of a computer to input information and generally annotate the records. While such a computer system might be efficient for someone who can type and is familiar with computer operating systems, it is difficult to operate efficiently for individuals who cannot type and who are not familiar with computer operating systems. Further, for physicians who are accustomed to using paper charts, it has been found that it is difficult to convert them to using an electronic system, especially if they are not particularly skilled at typing and using computer operating systems.
It is an object of the present invention to provide a light pen device that provides a more natural method of interacting with a computerized device.
Prior Art
Known prior art, which describes previous devices having, in each case, at least some of the shortcomings discussed above, includes the following United States patents:
U.S. Pat. No. 4,318,096, issued Mar. 2, 1982, to THORNBURG et al, discloses a graphics pen for soft displays, wherein a graphics input device is used with location indicating means to present graphic data upon a computer controlled visual display. The device includes a pen having a housing, within which housing is a conductive stylus shaft, one end extending beyond the housing to serve as the writing tip. A cylindrical off-axis pressure transducer encircles a portion of the stylus shaft within the housing, adjacent its writing end, for generating a variable output electrical signal proportional to the variable off-axis force applied to the stylus independently of the rotational orientation of the pen. A display processing and control system receives the variable signals and modifies a visual characteristic of the graphic data in response thereto.
U.S. Pat. No. 4,405,921, issued Sep. 20, 1983, to MUKAIYAMA, discloses a liquid crystal display device including a liquid crystal panel and a pen. The liquid crystal panel includes a plurality of display dots defined by spaced electrodes having a twisted nematic crystal therebetween. The display dots are selectively driven by a drive circuit between light-transmissive and non-transmissive states in a predetermined flickering timing. The light pen selectively directs light to the display dots which is caused to flicker thereby. The flickered light is detected by a sensor in the light pen and produces positioning data signals representative of the sequence of dots selected.
U.S. Pat. No. 4,705,942, issued Nov. 10, 1987, to BUDRIKIS et al, discloses a pressure sensitive light pen including a transparent rod at its pointing, through which light is directed to a photodetector that is fixedly positioned within the light pen. The rod is spring loaded and axially slidable in response to applied pressure, resulting in different light intensities being applied to the photodetector and further resulting in an output voltage generated by the photodetector, which output voltage is directly related to the applied pressure.
U.S. Pat. No. 5,646,650, issued Jul. 8, 1997, to MILLER et al, discloses an electronic paintbrush and color palette which allow a user to generate images on a CRT screen in a manner which imitates traditional painting with paints on a canvas. The electronic paint brush has fibre optic bristles which channel light from a CRT screen to optical detectors. A microprocessor in the brush utilizes pulses generated by the incidence of the raster scan on photodiodes to determine the position of the brush, the pressure of the brush on a CRT screen, and its angular orientation about the longitudinal axis of the brush. There is absolutely no co-relation between the color of the light received by the brush and the subsequent position of the brush while painting on the screen. The microprocessor utilizes color information generated by a CCD array to determine the area of contact of the brush with color swatches on the palette, and the angle between the longitudinal axis of the brush and the normal vector to the CRT screen. There is absolutely no co-relation between the color of the light received by the brush and the subsequent position of the brush while painting on the screen. In an alternative embodiment, the palette is also displayed on the CRT screen.
A position sensing system that is used is used to determine the track of an element over a pattern sequence is taught in BURNS et al U.S. Pat. No. 5,675,129, issued Oct. 7, 1997. Here, a sensing head or element is movable relative to a pattern which has pattern features that are established in respect of differences among the pattern features in directions which are parallel to a predetermined axis. A windowing property is thereby established; and, by sensing the pattern features traversed by the sensing element and comparing window-length portions of the succession of features with a stored representation of the overall series of features, it is possible sooner or later to detect an initial location of the element along the series of patterns. Having eventually detected the initial location of the element, further movement of the element can then be tracked incrementally. The initial track portion of the element can be back-tracked.
U.S. Pat. No. 5,477,012 issued Dec. 19, 1995 to SEKENDUR, teaches a co-ordinate sensor for detecting the position of a movable detector relative to a data-space which is coded with coordinate information. The coordinate information is detected and processed by the movable detector; however, the data-space must be preformatted with very complicated codes by which the coordinates of any point in the data-space can be determined. The detector detects the code, and thus the position of the detector in the data-space is determined. Thereafter, angular, rotational, or linear motion of the detector element may be determined, such as by handwriting on the coded tablet, on which additional handwritten data may be inscribed.
Each of SHELL U.S. Pat. No. 4,691,199 issued Sep. 1, 1987 and LYON U.S. Pat. No. 4,521,773 issued Jun. 4, 1985 teaches a type of hand held mouse which can be used to control the position and movement of an on-screen curser. In each case, a mouse-like object having a light source and a light detector are employed. In the case of SHELL, the mouse is moved over a tablet having an encoded grey scale imprinted thereon, so that movement from one area having a particular grey scale to another area having a different grey scale can be detected, decoded, and utilized so as to cause corresponding movement of the on-screen computer curser. In the LYON device, specific bit map images are determined, by way of a contrasting pattern which comprises a plurality of features on a contrasting background, over which the mouse is moved.